To protect and defend military platforms, such as ships, aircraft, and ground-based installations, it is known to provide countermeasure systems that detect incoming threats such as enemy aircraft or missiles. Known systems detect incoming threats, such as infrared missiles, and then deploy defensive countermeasures in an attempt to destroy or divert the threat. These systems are referred to as open-loop systems since no immediate determination as to the type of threat or effectiveness of the countermeasure is readily available. Due to the inefficiency of the open-loop systems, closed-loop systems have been developed.
There are known performance benefits to using a directional, laser-based, closed-loop infrared countermeasure system to defeat infrared missiles. In a closed-loop system, the incoming missile is identified and the countermeasure system generates or tunes a jam code according to the specific incoming missile. The optimized jam code is directed at the missile which executes a maximum turn-away from its intended target. An additional feature of closed-loop techniques is the ability to monitor the classification and identification process during the jamming sequence. This provides a direct observation of the countermeasure effectiveness as well as an indication of the necessary corrective action required for the jam code. It will be appreciated that the benefits of the closed-loop performance system must be balanced against the cost of upgrading existing infrared directional countermeasure systems with a closed-loop capability, or against the cost of developing an entirely new closed-loop system.
One possible configuration for introducing a closed-loop receiver into a directional countermeasure system is to use a high resolution tracking sensor side-by-side with an infrared detector assembly. Accordingly, an independent receive channel, which is a separate optical path, must be added to the detection system with a separate expensive cooled detector. The cost and size impact of such a configuration to the countermeasure system is prohibitive.
Although effective, the above device has limited coverage area. In particular, it is believed that the maximum field of regard for such a device and other known prior art devices is 120°. These devices are constrained by the internal optical components and their mechanical movement. Additionally, these prior art systems require the use of slip rings for connection between the rotating and fixed components. As will be appreciated by those skilled in the art, slip rings introduce noise and they may wear over a period of time resulting in unreliable signals and improper guiding of the optical signals.
In some prior art systems only a 180° pivotable movement of the pointer was needed to obtain a 120° field of regard. However, such devices provide inadequate scanning coverage in the nadir area of interest. In other words, the area immediately above or below the scanning device is not easily observed. Obtaining continuous coverage whenever a detected object passes through nadir adds complexity to the mechanical and optical components. These complex solutions have proven to be quite costly and yet no device has been found that rapidly scans and accurately points an optical transmit/receive beam over more than 2π steradians using a single compact, lightweight, low-cost, beam-steering device. Therefore, there is a need in the art for a scanner/pointer device with improved coverage and which has simplified mechanical interconnections.